EVAPORATION:
The process in which liquids convert into a gases phase is termed as evaporation
or
The type of vaporization that occurs at the surface of a liquid as it changes into gases phase.
For example: clothes dry under the sun due to evaporation, in this process water is converted from liquid state into vapors by acquiring heat from sun.
How evaporation occurs in liquids?
The molecules of liquids are in continuous motion they collide with each other but all the molecules do not have same kinetic energy. Majority molecules have average kinetic energy and few have more than average kinetic energy.
The molecules having more than average kinetic energy overcome the attractive forces among the molecules and escape from the surface evaporation. It is directly proportional to temperature and increase with the increase in temperature.
Why evaporation is a cooling process?
The evaporation is also considered as cooling process because when high kinetic energy molecules escape in the air in the form of vapors. The temperature of remaining molecules falls down. To compensate this deficiency of energy molecules absorb energy from the surrounding, due to which temperature of surrounding decreases and feel cold.
FACTORS AFFECTING EVAPORATION:
Surface Area: Evaporation is directly proportional to the surface area of the liquids. Greater the surface of the liquids faster will be the evaporation and vice versa. For example: water left in bowl evaporate slowly than water spread on the floor.
Temperature: Evaporation is directly proportional to the temperature of the liquids. An increase of temperature increases the kinetic energy of liquid particles as a result of which their rate of evaporation increases and vice versa. For example: clothes dry quickly in a sunny day than a cloudy day.
Intermolecular Forces: Evaporation is inversely proportional to the intermolecular forces of attraction of the liquids. Liquids with strong intermolecular forces evaporates slowly as compared to liquids with weak intermolecular forces. For example: perfume have weak intermolecular forces than water therefore it evaporates quickly.
VAPOR PRESSURE:
The pressure exerted by vapors, at particular temperature when they are in equilibrium with their liquid state, is termed as vapor pressure.
or
The pressure exerted by vapors when rate of evaporation becomes equal to rate of condensation.
How vapor pressure is exerted by liquids?
Consider a liquid in a closed container. Initially, there are no vapors in the empty space above the surface of the liquid. When the temperature of a liquid rises, it starts evaporating, and its vapors are gathering above the surface of the liquid. The vapors are converting back into the liquid by loosing a part of their kinetic energy. Since the rate of evaporation is higher than the rate of condensation, therefore, with the passage of time, more and more vapors are accumulated in the space. This will finally equalize the two rates. Hence the equilibrium is achieved.
At this state the vapor molecules, due to their continuous state of random motion, collide with the wall of the container and exert pressure on it. This is the vapor pressure.
FACTORS AFFECTING VAPOUR PRESSURE:
Nature of Liquid: The vapor pressure depends upon the nature of liquids .Polar liquids have low vapor pressure than nonpolar liquids at the same temperature. It is because of strong intermolecular forces of molecules and high boiling point in the polar liquids. For example: water (a polar liquid) has less vapor pressure than alcohol (a non- polar liquid).
Size of Molecules: The vapor pressure is inversely proportional to the size of molecules of liquids. The smaller the size of liquid particles the higher will be vapor pressure because they evaporate quickly and vice versa. For example: hexane (\ce {C6H14}) has a small size of molecules as compared to decane (\ce {C10H22}), due to this hexane evaporate rapidly and exert more pressure.
Temperature: The vapor pressure is directly proportional to the temperature of liquids. The average kinetic energy of molecules increases with temperature which causes increase in vapor pressure and vice versa. For example: vapor pressure of water at 0 C is 4.58 mm Hg while at 100 C it increases up to 760mm Hg. (mmHg= milli meter of mercury).
BOILING POINT:
The temperature at which the vapor pressure of a liquid becomes equal to the atmospheric pressure (external pressure) and the liquid changes into a vapors, is termed as boiling point and such phenomenon is called boiling.
FACTORS EFFECT THE BOILING POINT:
Atmospheric Pressure: The boiling point is directly proportional to atmospheric pressure. It means that the increase in atmospheric pressure will increase the boiling point of a particular liquid. For example; the working of pressure cooker, which applies more external pressure during the cooking of meal.
Nature of liquid: Polar liquids have high values of boiling points due to strong forces of attraction between their molecules as compared to non-polar liquids. For example: Boiling point of water (a polar liquid) has high boiling point i-e 100 C as compared to di ethyl ether (a non-polar liquid) i-e 34.6C.
Intermolecular forces of attraction: Boiling point is directly proportional to intermolecular forces of attraction. Liquids with strong intermolecular forces exert a level of vapor pressure at high temperature and vice versa.
FREEZING POINT: “The temperature at which the vapor pressure of a liquid state becomes equal to the vapor pressure of its solid state is known as Freezing Point of a liquid.” At this temperature liquid and solid coexist in dynamic equilibrium.
FACTORS AFFECTING FREEZING POINT:
The freezing point depends upon the temperature and intermolecular forces. Molecules with stronger intermolecular forces are pulled together to form a solid at high temperature. Due to this they show high temperatures for freezing point. Molecules with lower intermolecular forces solidify on lower temperatures.
For example: The freezing point of water (liquid with strong intermolecular forces) is 0.0 C whereas the freezing point of ethyl alcohol (Liquid with weak intermolecular forces) is -114 C.
DIFFUSION:
The mixing of two or more substances so as to form a homogeneous mixture is called diffusion
or
The spreading of particles from area of higher concentration to lower concentration, is termed as diffusion.
For example;
a drop of a dye or any colored solution diffuses through water.
According to kinetic molecular theory, the liquid molecules are in cluster form and are closer to each other i-e one layer upon another. This is due to:
Strong attractive forces bind them as compared to gases.
Their particles are fairly free to move as compared to gases.
Hence the molecules of liquids can diffuse into one another but the rate of diffusion in liquids is slower than the gases.
FACTORS AFFECTING DIFFUSION:
Size of molecules: Liquids with huge size molecules diffuses slower than that of liquids with smaller size molecules. It means that diffusion of liquids is inversely proportional to size of molecules.
Shape of molecules: Liquids with regular shapes of molecules diffuses faster than that of liquids with irregular shapes of molecules.
Intermolecular forces of attraction: Liquids diffuses faster than solids but slower than gases due to moderate forces of attraction present between liquid particles as compared to gases and solids.
Temperature: Diffusion of liquids is directly proportional to temperature because increase in temperature increases the kinetic energy of molecules and they diffuse with faster rate and vice versa.
MOBILITY:
The ability of particle to move freely is termed as mobility.
The molecules in a liquid move freely, due to free movement they can adjust their shapes in a container. Due to this reason liquids can flow.
FACTORS AFFECTING MOBILITY:
Temperature: Temperature is directly proportional to mobility of liquid particles. Mobility increases by increasing the temperature. When temperature increases in a liquid, movement of molecules increases accordingly with the increase of kinetic energy and vice versa.
Inter molecular forces: Mobility of liquid molecules is inversely proportional to intermolecular forces. Mobility increases by decrease in intermolecular forces. The liquids which have strong intermolecular forces show less mobility of molecules and vice versa.
DENSITY:
Mass per unit volume is termed as Density.
Liquids are denser than gases due to closely packed molecules and weak intermolecular spaces. As the closely packed molecules of liquids have strong intermolecular forces they cannot expand freely and shows definite volume which makes liquids denser than gases.
Mathematically:
Density = mass/ volume or D = m /v
Unit: D = grams / cubic deci meter or
D = g / dm or g / L
FACTORS AFFECTING DENSITY:
Temperature: liquids are less affected by the temperature as by increasing temperature liquids increase their volume which decrease density. Different densities of water at different temperature are given below.
Pressure: liquids are slightly affected by pressure .Increase in pressure of liquids increases the density, but liquids are not readily compress due to which, change of density is negligible.
